American officials are sending an investigator to Alberta to look into how a cow on a farm south of Edmonton was infected with mad cow disease.

It's the seventh Canadian cow to test positive for bovine spongiform encephalopathy.

Unlike a recent BSE case in Manitoba, the Alberta cow was born after 1997, when Canada imposed a ban on the type of feed associated with BSE.

The U.S. Department of Agriculture said Thursday it would send an inspector to aid in the investigation into the Alberta case.

Agriculture Secretary Mike Johanns said there are unanswered questions.

"We need a thorough understanding of all the circumstances involved in this case to assure our consumers that Canada's regulatory system is effectively providing the utmost protections to consumers and livestock," Johanns said.

'Keep the politics at bay'

The Montana-based R-CALF United Stockgrowers of America argued in a release issued Thursday that Canada's BSE problems are hurting the reputation of American beef.

Alberta Beef Producers chairman Darcy Davis said Thursday the American reaction concerns him, especially since the U.S. has congressional elections this fall.

"We're trying to base things on sound science, and as long as we stick to sound science, hopefully we can keep the politics at bay," he said.

Cow didn't die of BSE

The Canadian Food Inspection Agency has quarantined the farm and is doing BSE testingon other cows born within a year of the dairy cow.

Alberta's chief veterinarian, Gerald Ollis, said the four-year-old Edmonton-area cow actually died of something other than BSE.

"It wasn't exhibiting any signs that would make you think it was BSE," he said. "It's quite likely she died of something other than BSE, and BSE has just been discovered as an incidental finding."

The agency has said the Alberta cow could have been infected by cattle feed that had accidentally been mixed with another animal's feed in a bin.

Other countries have also discovered BSE cases after feed bans are put in place, the agency argues.

Ollis expects more cases of BSE to turn up in Canada because infected materials are still being found on troughs of feed lots and conveyor belts in feed plants.

New classification

Internationally, BSE has been linked to a deadly type of Creutzfeldt-Jakob disease among humans who have eaten certain types of tissues from infected cows.

A discovery of BSE in an Alberta cow in 2003 threw the country's cattle industry into chaos. Many countries closed their borders to imports of Canadian cows or beef in the wake of the discovery.

However, in December 2004, the U.S. Department of Agriculture announced that it recognized Canada as a "minimal-risk region."

The new classification means the U.S. will not close its borders again to Canadian beef unless there are two or more cases of BSE per one million cattle older than 24 months in each of four consecutive years.

With files from the Associated Press